The invention relates generally to the field of draft appliances for vehicles and, more particularly, to draft appliances which are suitable for agricultural uses, such as between a tractor and a pulled farm implement.
When a tractor is used to pull a typical farm implement, such as a planter or plow, over a field in order to perform normal farming operations, it is important to keep the planter in a level or untilted position with respect to the ground. For example, if the planter is tilted the resulting furrow will be uneven in depth, which for planting purposes is an undesirable condition. As long as the tractor and planter are not tilted with respect to each other, an incline or decline may be traversed without problem. However, when the tractor and planter are tilted relative to each other, the pulling action of the tractor will tend to tilt the planter with respect to the ground immediately below it. The result is that during the periods of relative tilt between the tractor and the planter, the furrow will be either deeper or more shallow than is desirable. Since a desirable furrow may be only several inches deep, relatively shallow grades can produce significant changes in the depth of the furrow. Thus, even though a typical field will not have any abrupt changes in slope, most fields will have slope changes significant enough to prevent an even depth furrow to be dug by the planter when normal equipment is used.
The following list of references disclose devices which apparently offer certain improvements in couplings between vehicles.
______________________________________ U.S. Pat. No. Inventor ______________________________________ 1,908,711 Kuchar 1,259,205 Bessesen 2,011,817 Littlefield 1,796,087 Day et al. 2,168,148 Arehart 1,356,270 De Saunier 1,267,561 Lapham ______________________________________
The above devices all provide couplings which permit a certain amount of flexibility so that lateral and torsional forces exerted upon the couplings will not easily break it, and also a shock absorbing effect is produced at the coupling. None of these couplings however provide any structure which is adaptable to farm equipment for ensuring an even depth of the furrow when the tractor and planter are tilted with respect to each other.
U.S. Pat. No. 2,159,253 to Bush discloses a trailer hitch which is presumably designed to provide control over certain relative movements between the transporting vehicle and the trailer, especially those movements which occur during backing of the trailer preparatory to parking. The structure however, is not adaptable to controlling or compensating for forces exerted on a coupling which tend to cause a planter to dig an uneven furrow.
U.S. Pat. No. 2,710,514 to Broussard discloses a coupling device which attempts to solve problems caused by relative tilt between a tractor and a pulled vehicle or implement. Thus, Broussard discloses an implement tongue and track assembly which apparently permits a pulled vehicle to ride over steep inclines and obstructions without an upward movement of the coupling. This device however, is not able to correct tilting problems so as to permit digging a furrow having a constant depth.
U.S. Pat. No. 3,032,903 to Ede discloses a supporting linkage arrangement for a mole plow which presumably enables the mole to operate in floating equilibrium at a constant depth relative to the vehicle. This device however, is not adaptable for use on a pulled vehicle, such as a planter, in order to provide a constant depth furrow when the tractor and pulled vehicle are tilted relative to each other.
Accordingly, it is an object of the present invention to provide an improved drawbar apparatus which is suitable for use between a planter and tractor for permitting a planter to dig a furrow having a constant depth.